1. Field of the Invention
The present invention relates to phase commutation control over inductive motors and more particularly to a speed regulation system, which by means of a linearized phase commutation of a linear inductive motor, controls the speed of a vehicle.
2. Description of the Prior Art
Induction motors, both linear and rotary type, were often controlled in the past to a desired torque output through well known phase commutation techniques. Such phase commutation techniques have been typically nonlinear in character, since the conventional timing increments which correspond to phase angle increments of an A.C. signal are usually in evenly distributed increments and the corresponding torque output or propulsive output increments of the motor follow a sine function of the signal commutated for any given torque control signal. Accordingly, as linear increments of phase are taken to commutate the motor, the resulting force or torque output follows a sine curve and phase angle increments occurring close to the 0.degree. or 180.degree. crossing of the since wave are therefore lower in torque than the commutation increments occurring close to the maximum of the signal sine wave. This particular feature of phase commutation has been partly met in some linear systems by appropriately shaping the reference signal against which phase commutation takes place. In prior art digital applications, however, such convenience is not normally available since typically phase commutation is accomplished according to a fixed increment clock.
Digital control systems, on the other hand, provide a plurality of known beneficial features which have been successfully utilized in the past and which typically trade off over the linear character or linear performance of the control system.
One particular application for such phase commutating control systems is automatic speed control of a linear inductive motor propelled vehicle. Such applications of vehicle propulsion when further adapted for use in amusement parks for conveying spectators include further variables where the vehicles may be loaded to various weights or where trains of various lengths are utilized. This utilization of vehicles loaded to various weights drive along a spectator guideway provides a variable which must be controlled, in synchronism with other trains, by conventional feedback techniques. In prior art, vehicle speed has been measured by measuring axle or wheel rotation. The measured speed was then compared against a desired speed and appropriate corrections were taken through selective phase commutation of the motor. Prior art systems of this kind usually involve a configuration where a part of the track or the guideway forms the secondary or the platen of the linear induction motor while the inductor itself is located within the vehicle body. While such configurations are economical in terms of the number of inductors required, they typically entail a third track which is energized and from which power is continually drawn by the vehicle or train. Since spectator guideways are often located in common with public foot paths, such third rail which is constantly energized often exposes the local pedestrians to hazard.